Electrochemical and Structural Investigation of the Mechanism of Irreversibility in Li 3 V 2 (PO 4 ) 3 Cathodes

High Resolution Image Download MS PowerPoint Slide Lithium-ion batteries dominate the battery field, particularly for electric and hybrid vehicles. Monoclinic Li 3 V 2 (PO 4 ) 3 has emerged as one of the most promising candidates for the cathode in lithium-ion batteries, offering better environmental safety and lower cost than competing materials. We have used in situ X-ray absorption spectroscopy to characterize the evolution of the vanadium in a Li 3 V 2 (PO 4 ) 3 cathode as it is cycled electrochemically. These data demonstrate the presence of significant kinetic effects such that the measured electrochemical behavior does not represent the bulk vanadium. When the cell is cycled between 3 and 4.5 V, there are two distinct vanadium species. When the potential is raised above 4.5 V, a third species is observed, consistent with formation of V 5+ . XANES data for the cathode after 3–4.8 V cycling are consistent with a severely distorted vanadium site, suggesting that lithium–vanadium antisite mixing may be responsible for the electrochemical irreversibility that is seen above 4.5 V.